An electric power source system for a vehicle includes multiple kinds of storage batteries, such as lead-acid batteries and lithium-ion batteries. These different kinds of storage batteries properly supply power to different electrical loads equipped to the vehicle.
For example, as disclosed in JP 2012-130108 A, a lead-acid battery and a lithium-ion battery are connected with each other through a switch. Some of the electrical loads in the vehicle need to be supplied with stabilized electric power. Herein, stabilized electric power is a power that has a constant voltage or a voltage fluctuating only within a predetermined range. These kinds of electrical loads are connected to the lithium-ion battery. In this configuration, the lithium-ion battery provides power supply to the electrical loads, which require the stabilized power supply. Among the electrical loads, except the electrical loads, which require the stabilized power supply, a starter motor and other general electrical loads, such as headlamps are connected to the lead-acid battery. In this configuration, the lead-acid battery provides power supply to the starter motor and other general electrical loads.
In the above-described configuration, when the lead-acid battery has an operation failure, the lead-acid battery cannot supply power to the general electrical loads connected thereto. Similarly, when the lithium-ion battery has an operation failure, the lithium-ion battery cannot supply stabilized power to the electrical loads that require the stabilized power supply. Accordingly, operation failures or abnormalities may occur to the electrical loads that require the stabilized power supply.